Radiation source simulation means

ABSTRACT

Advanced sensor evaluation and test apparatus comprises a vacuum chamber with an inner cryoshroud, housing an on-axis optical parabolic collimator, a radiant energy source assembly having an output aperture located in the focal plane of the collimator, a calibration monitor consisting of a Cassegrainian type radiometer that occupies one portion of the collimated radiant energy beam and which forms an image of the source on a bolometer, and a pair of scanning mirrors directing energy from another portion of the collimated beam into the entrance aperture of the optical sensor under test. In addition, a background radiant energy generator can direct radiant energy simulating elevated radiation background to the sensor under test which, in turn, forms an enlarged image of the background source in its own detector plane. One version of the source assembly includes at least one blackbody radiation source of variable aperture and temperature with a chopper operating to provide modulated radiation which is projected into an integrating sphere coupled with a source projector. An adjustable dual reflector with one specularly and one diffusely reflecting surface is mounted inside the integrating sphere and can be rotated to predetermined orientations to function in either a specularly reflecting mode or diffusely reflecting mode. In a third mode of operation, the mirror is rotated into an inactive orientation in which it does not intercept the beam entering the integrating sphere. This is the integrating sphere mode of operation. Another version of the source assembly includes at least one blackbody radiation source providing radiation to an integrating sphere coupled with a radiation guide (pipe). The radiation guide can be either a single or dual guide (pipe) and is cooperatively structured to operate with selected transmission patterns (transparent portions) on a movable disc sector positioned at the end of the guide.

United States Patent [191 Meier Nov, 27, 1973 RADIATION SOURCESIMULATION MEANS [75] Inventor: Rudolf H. Meier, Santa Ana, Calif.

[73] Assignee: McDonnell Douglas Corporation,

Santa Monica, Calif.

[22] Filed: Aug. 24, 1972 211 Appl. No.; 283,518

Primary Examiner-James W. Lawrence Assistant Examiner-Davis L. WillisAttorney-Walter J. Jason et al.

[ 5 7 ABSTRACT Advanced sensor evaluation and test apparatus comprises avacuum chamber with an inner cryoshroud, housing an on-axis opticalparabolic collimator, a radiant energy source assembly having an outputaperture located in the focal plane of the collimator, a calibrationmonitor consisting of a Cassegrainian type radiometer that occupies oneportion of the collimated radiant energy beam and which forms an imageof the source on a bolometer, and a pair of scanning mirrors directingenergy from another portion of the collimated beam into the entranceaperture of the optical sensor under test. In addition, a backgroundradiant energy generator can direct radiant energy simulating elevatedradiation background to the sensor under test which, in turn, forms anenlarged image of the background source in its own detector plane. Oneversion of the source assembly includes at least one blackbody radiationsource of variable aperture and temperature with a chopper operating toprovide modulated radiation which is projected into an integratingsphere coupled with a source projector. An adjustable dual reflectorwith one specularly and one diffusely reflecting surface is mountedinside the integratingsphere and can be rotated to predeterminedorientations to function in either a specularly reflecting mode ordiffusely reflecting mode. In a third mode of operation, the mirror isrotated into an inactive orientation in which it does not intercept thebeam entering the integrating sphere. This is the integrating spheremode of operation. Another version of the source assembly includes atleast one blackbody radiation source providing radiation to anintegrating sphere coupled with a radiation guide (pipe). The radiationguide can be either a single or dual guide (pipe) and is cooperativelystructured to operate with selected transmission patterns (transparentportions) on a movable disc sector positioned at the end of the guide.

18 Claims, 12 Drawing Figures PAIENTEnnnvznm q 775 620 SHEEI 5 OF 6PMENTEI] NUVZ 71975 sum 6 OF 6 RADIATION SOURCE SIMULATION MEANSBACKGROUND or THE INVENTION This invention relates generally toenvironmental test apparatus and, more particularly, to novel componentsand combinations of components in an advanced sensor evaluation and testapparatus for testing, under exoatmospheric conditions, components,subsystems and systems having the capability of generating and/orcollecting and processing radiant energy.

With the advent of increased space flight and anticipated long rangespace missions in the foreseeable future, a greater need has developedfor'testing electrooptical (radiant energy) components, subsystems andsystems under idealized testing conditions closely duplicating actualexoatmospheric environmental .flight conditions. In order to measure.certain test parametersof interest of, for example, aradiant energysensor or of its detector-amplifier subsystem, a suitable source ofmodulated or constant level radiant energy is desirably provided tooperate (excite) thedetectionmeans under appropriate environmentaltemperature and vacuum conditions. The source, moreover, must ordinarilyappear to the detection means to be located at infinity, and maycomprise single or multiple'point sources and- /or extended sources forboth spatially static and dynamic target simulation. Of course, thenoise equivalent flux density (NEFD) of the detection means must beestablished only by the inherent noise of the detector and itsassociated electronic. circuitry. Absolute measurement andcalibration oftotal and. spectral properties of the detection means or othercomponents are also required to provide adequate evaluation thereof.

SUMMARY OF THE INVENTION Briefly, and in general terms, the inventionincludes a vacuum chamber with a vertical penetration, an innercryoshroud, an on-axis folded parabola optical collimator contained inthe cryoshroud, a radiant energy source assembly (of differentselectable versions) having an output aperture located in the focalplane of the collimator, a calibration monitor consisting of aCassegrainian type radiometer occupying one portion of the collimatedbeam and forming an image of the source on a bolometer, and a pair ofscanning mirrors directing energy from another portion of the collimatedbeam into the entrance aperture of thesensor under test mounted in thechamber vertical penetration. Also, a background radiant energygenerator can direct radiant energy simulating elevated backgroundradiation into the entrance aperture of the sensor under test which, inturn, forms an enlarged image of the background source in its owndetector plane.

More specifically, one version of the radiant energy source assemblyincludes a backbody radiation source of variable aperture andtemperature with a chopper operating to provide modulated radiationwhich is projected into an integrating sphere coupled via a variableaperture with a source projector. An adjustable dual reflector with onespecularly reflecting surface and one diffusely reflecting surface ismounted inside the integrating sphere and can be rotated topredetermined orientations to function in either a specularly reflectingmode or a diffusely reflecting mode. In a third mode of operation ofthis version of the source assembly, the mirror is rotated into aninactive orientation in which it does not intercept the beam enteringthe integrating sphere. This mode is called the integrating sphere modeof source operation. Another source assembly version includes ablackbody source providing radiant energy to an integrating spherecoupled with aradiation guide (pipe). The radiation guide can be eithera single or dual guide and is cooperatively structured to operate withselected transmission patterns (transparent portions) on a movable discsector positioned just before the end of the guide. Yet another sourceassembly version is a universal one which is generally similar to thefirst version described above but is implemented and arranged in amanner to be further capable of functioning electively as amonochromator type source assembly.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fullyunderstood, and other features and advantages thereof will becomeapparent, from the description given below of certain exemplaryembodiments of the invention. This description of the exemplaryembodiments of the invention is to be taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a simplified elevational view, shown somewhat diagrammaticallyin section, of an illustrative advanced sensor evaluation and testapparatus con structed in-accordance with this invention;

FIG. 2 is an end elevational view of the test apparatus as taken alongthe line 2-2 indicated in FIG. 1;

FIG. 3 is a top plan view, somewhatdiagrammatically shown in section, ofone version of a radiant energy source assembly used in the testapparatus depicted in FIGS. 1 and 2;

FIG. 4 is an enlarged sectional view of the integrating sphere structureused in the radiant energy source assembly of FIG. 3;

FIG. 5 is a simplified perspective view of a pair of scanning mirrorsdirecting radiant energy to a sensor and a background radiant energygenerator cooperatively providing controlled background radiant energyover the entire area of the sensors detector plane;-

FIG. 6 is a side elevational view, shown partially in section, ofanother version of a radiant energy source assembly cooperativelystructured to operate with a movable disc sector positioned just beforethe end of a dual radiation guide of the source assembly;

FIG. 7 is a front elevational view of the movable disc sector shown inFIG. 6;

FIG. 8 is a front elevational view of the end of a single radiationguide which is cooperatively structured to operate with the transmissionpattern (transparent portions) of a movable disc sector indicated inphantom lines before the end of the guide;

FIG. 9 is a front elevational view of the movable disc sector indicatedin phantom lines in FIG. 8;

FIG. 10 is a top plan view, shown somewhat diagrammatically in section,of a schematic layout of a monochromator type source assembly;

FIG. 11 is a simplified elevational view, somewhat schematically shownin section, of a spectrometer attachment for making spectralmeasurements; and

FIG. 12 is a top plan view, shown somewhat diagrammatically in section,of a universal type source assembly.

DESCRIPTION OF THE PRESENT INVENTION In the accompanying drawings andfollowing description of certain exemplary embodiments of thisinvention, some specific dimensions, operating values and types ofmaterials may be disclosed. Such dimensions, values and types ofmaterials are, of course, given as examples only and are not intended tolimit the scope of the invention in any manner.

FIG. 1 is a simplified elevational view, shown somewhat diagrammaticallyin section, of an illustrative advanced sensor and evaulation testapparatus 20 constructed in accordance with this invention. The testapparatus 20 basically includes a vacuum chamber 22, an inner cryoshroud24, an on-axis optical collimator 26 comprising mirrors 28, 30 and 32contained in the cryoshroud, a radiant energy source assembly 34, andoptical and electronic instrumentation (not shown) required incalibration, test and evaluation of different sensors and variouscomponents of interest. Many of the elements of the test apparatus 20are conventional and are only diagrammatically shown without detail.This permits greater clarity of illustration of the novel arrangementand combination of elements. Of course, individual novel elements aredisclosed in adequate detail herein.

The vacuum chamber 22 is, for example, formed from a stainless steelhorizontal cylinder approximately 8 feet in diameter by 14 feet long,with a vertical penetration 36 which is 78 inches in diameter. Thevertical penetration 36 can be extended in height by stacking andsecuring spools (not shown) thereon to the desired height. Main accessto the interior of the chamber 22 is through the cylinder end normallyclosed by removable cover 38, and through the vertical penetration 36.Additionally, eight portholes or penetrations (not shown) 11 inches indiameter and a number of smaller penetrations (also not shown) aredistributed around the chamber wall. Vacuum levels of torr or better areachieved with a conventional contamination-free pumping system (notshown) which includes a mechanical roughing pump, a sorption pump, anion pump, a bulk titanium sublimation system and a turbo pump.

The cylindrical cryoshroud 24 is located inside the vacuum chamber 22and is, for example, approximately 7 feet in diameter by 10 feet long.The cryoshroud 24 is preferably made from extruded aluminum High ECryopanel (supplied by High Vacuum Equipment Corporation of Hingham,Mass), and the interior surface is ofa finned and serrated structurepainted with a flat black which provides an emissivity close to unity.The cryoshroud 24 is cooled by dual one kilowatt-capacity, gaseoushelium, closed cycle pumping systems (not shown), circulating therefrigerant through closely spaced passageways in the extruded panelstructure. The cryoshroud 24 is cooled to a temperature of approximatelyl(, for example, thereby providing an extremely low background radiationenvironment.

FIG. 2 is an end elevational view of the test apparatus 20 taken alongthe line 22 indicated in FIG. 1. The optical collimator 26 housed withinthe cryoshroud 24 is, for example, a 32-inch diameter, f/3.75 parabolic(mirror on-axis collimation system. The three mirrors 28, 30 and 32 ofthis 1 19-inch focal length collimation system are integrally mounted inthe positions illustrated on a framework constructed from series 6061T6aluminum tubing, The mirrors 28, 30 and 32 are, for example. fabricatedfrom series 300 aluminum material, Kanigen coated, and figured toprovide a diffraction limited system performance at all wavelengths ofinterest. To reduce cool-down time, the mirrors 28, 30 and 32incorporate an independent thermal control system includingcooling/heating coils (not shown) attached to their rear surfaces. Theentire cryoshroud 24 chamber and its contents can reach a stable 20Koperating temperature is approximately 16 hours.

A radiant energy source or target simulating assembly 34 is located atthe focal plane of collamator mirror 30 and radiates energy throughcentral opening 42 of mirror 32 into the collimator 26. The sourceassembly 34 is mounted on a support structure 44 which is adjustable toposition the source assembly in three dimensions about the focal planeof collimator mirror 30. In this instance, the support structure 44 isdiagrammatically illustrated as, for example, a stack of three platforms46 wherein the upper platform can be adjusted on rollers in a firsthorizontal dimension, the middle platform on rollers in a secondhorizontal dimension perpendicular to the first dimension, and the lowerplatform directly in a third dimension. Electric motors (not shown) canbe used to adjust the three platforms, respectively.

The collimator 26 collimates and directs the radiant energy from thesource assembly 34 in a 32-inch diameter beam as indicated by rays 48partly to a Cassegrainian telescope 50 and partly to a pair of scanningmirrors 52 and 54. The telescope 50 collects and images that portion ofthe collimated radiant energy which enters its aperture to a bolometer56 used for calibration purposes. The mirrors 52 and 54 are pivotablymounted on respective diameters in a beam deflector assembly 58 so thateach can be deflected about a single axis which is orthogonal to theother axis, either in an oscillatory mode or in a static mode. The drivemechanisms (not shown) can be selectively energized, varied respectivelyin speed (frequency) and amplitude, or synchronously driven. The mirror54 directs its reflected radiant energy into the entrance aperture ofthe sensor under test 60 which images the radiation source onto itsdetector plane 62 by representatively indicated optics 64. The sensor 60comprises, for example, a Cassegrainian telescope and a detector or(more normally) an array of detectors located at its focal plane, Thesensor 60 includes a cooling system (not shown) for maintaining itstelescope and detector array at desired and predetermined temperatures.A background generator 66 for providing broadly superimposed radiationto the detector plane 62 is indicated only in block form in FIGS. 1 and2 but will be shown and described in greater detail later.

FIG. 3 is a top plan view, somewhat diagrammatically shown in section,of one version 68 of the radiant energy source assembly 34 which can beused in the test apparatus 20 of FIGS. 1 and 2. The source assemblyversion 68 includes a conventional adjustable temperature blackbodysource 70 emitting radiation passing through a variable aperture in disc72 and is normally chopped by a chopper 74. The disc 72 can have anumber of differently sized and/or shaped apertures therein and can beremotely operated by a motor (not shown) to select any particularaperture. The chopper 74 can be a conventional chopper disc having oneor more tranparent sectors of suitable angular width and spacing, anddriven by a variable speed motor (not shown).

Since alternating current amplification is normally used with thedetectors of sensor 60 (FIG. 1), if chopper 74 is not employed then atleast one of the scanning mirrors 52 or 54 is oscillated to producemodulated output signals from the array detectors periodically excitedby the oscillating (moving) image of the simulated source. The sourceradiation is reflected by a plano mirror 76 and may be attenuated byadjustable attenuator 78. The attenuator 78 is an opaque metallic platewhich can be adjusted to different positions as indicated in brokenlines to intercept a portion or all of the radiation beam. The beam isfurther reflected by an off-axis refocusing mirror 80 and plano mirrors82 and 84 into an integrating sphere 86 through opening 88.

The integrating sphere 86 has a gold coated diffusely reflectinginternal surface 90 and another opening 92 which represents a variableexit aperture for the radiation in conjunction with a variable aperturedisc 94 located in its close proximity. Through this opening 92 theradiant energy enters the source projector 96. The disc 94 is rotatablymounted in housing 98 which has an opening 100 in registry with theopening 92 of integrating sphere 86 afflxed to the housing. The disc 94is similar to the disc 72 and can have a number of differently sizedand/or shaped exit apertures 93 therein and can be remotely operated toselect any particular exit aperture for the integrating sphere 86. Theexit aperture 93 is placed at the back-focus of the source projector 96which is, for example, a folded reflector telescope including aspherical converging mirror 102 and folding plano mirror 104 having acentral aperture 106 located at the focal plane of the collimator mirror30 (FIG. 1). The source projector 96 forms a demagnified image of theexit aperture 93 of the integrating sphere in the central aperture 106of folding plano mirror 104. Since this demagnified image is located inthe focal plane of the parabolic collimator 30, it represents the actualsimulated source of the apparatus.

FIG. 4 is an enlarged central sectional view of the integrating sphere86, clearly illustrating its internal structure. The integrating sphere86 mounts a rotatable plano mirror 108 inside it on a shaft 110. The(metallic) mirror 108 has a specularly reflecting surface on one sideand a diffusely reflecting surface on the opposite side. The shaft 110extends outside of the sphere 86 and can be rotated by a motor (notshown) to adjust the mirror 108 to the positions indicated in solid andbroken lines. In the solid line position of the mirror 108 as shown inFIG. 4, the specularly reflecting surface is normally used to direct theimage formed by off-axis refocusing mirror 80 of the source aperture indisc 72 onto aperture 93 at the back-focus of the source projector 96.The source projector 96 then forms a demagnified secondary image of thesource aperture at the focal plane of the collimator mirror 30 (FIG. 1In the diffuse mode of operation, mirror 108 is rotated 180, such thatits diffusely reflecting side comes into action. In this mode, dependingon the degree of diffusion, the radiant flux which leaves theintegrating sphere 86 within the useable acceptance angle of the sourceprojector 96, is reduced by one to two orders of magnitude.

For the integrating sphere mode of operation, however, the mirror 108 isplaced in the broken line position with its diffused reflecting surfacefacing the exit aperture 93. The mirror 108 is oriented approximatelyperpendicular generally to the axis of the source projector 96 (and thesphere opening 92) and does not act as a beam deflector, thus providingpurely integrating sphere type output in such position. The sphere 86functions more effectively by the addition of an internal convexdiffused surface portion 87 which is positioned to reflect (scatter) theincoming radiation up-, wardly towards the opening 92. The diffusedsurface of mirror 108 facing the opening 92 further reflects anyradiation back towards the opening 92. For a nominally 3-inch diametersphere 86, for example, the convex portion 87 can be formed by insertingand welding a segment of a A-inch diameter sphere into a 5/l6-inch holein the sphere 86. The convex portion 87 is, of course, also diffuselygold coated. The mirror 108 can be, for example, approximately l-inch byl-inch.

In the integrating sphere mode of operation, the source output is againreduced by two to three orders of magnitude as compared to the diffusereflection mode of operation. Also, in this mode, attenuator 78 (FIG. 3)can be applied for additional controlled radiant energy reduction byanother two orders of magnitude. It is noted that the source projector96 is carefully baffled by baffles 112 and 114 to obviate any problemsdue to scattered radiant energy. The major unique advantage of sourceassembly version 68 is that its radiant exitance can be varied by purelymechanical means over a wide dynamic range (10) without the applicationof filters or unduly small apertures and with no change of its spectralsignature. The amount of radiant energy leaving opening 92 is simplycontrolled by the operational mode (position) of mirror 108, by aperturecombinations and by the position of attenuator 78.

FIG. 5 is a simplified perspective view of the Cassegrainian typetelescope 50 with bolometer 56, the pair of scanning mirrors 52 and 54,the sensor under test 60, and the background generator 66. Thebackground generator 66 includes a blackbody source 116, a filter wheelassembly 1 18, a short focal length Cassegrainian type collimatorconsisting of mirrors 122 and 124, and a plano reflector 126. The wheelassembly 118 can be selectively set or be rotated either in steps orcontinuously by motor 119. The wheel assembly 118 can thus adjust orvary the=radiant energy in a predetermined manner by appropriate choiceand sequence of filters mounted therein. The filters can, of course, betempoarily removed from the wheel assembly 118 which can then be rotatedto serve as a form of chopper, or a conventional chopper (not shown) formodulation of the radiant energy emitted by the source 116 can beprovided, for example, directly before the output of the source ordirectly after the wheel assembly. All of these elements of thebackground generator 66 can be suitably mounted to associated structureof the large collimator 26 (FIG. 1). 1

Plano reflector 126 deflects the collimated radiant energy from thebackground generator source 1 16 in a direction parallel to thecollimated beam of the collimator 26 within the beam cross section(aperture) occupied by the pair of scanning mirrors 52 and .54, suchthat the background radiant energy enters the aperture of the sensorunder test 60 near its edge. Sensor 60 in turn forms with its ownimaging optics 64 (FIG. 1) a much enlarged image of the. aperture of thebackground source 1 16 which covers its own entire detector plane 62.The size of the image of the background source aperture as focused onthe detector plane is equal to the background aperture size enlarged(magnified) generally in proportion to the ratio of the focal length ofthe sensor optics 64 to that of the collimator 120 (i.e., mirror 122 inFIG. Since the enlarged background aperture image uniformly covers theentire detector array, any background image motion caused by one of thescanning mirros 52 or 54 (when used) does not produce any significantmodulated output signals from any of the array detectors due to suchmotion. Source 116 and the filters of the filter wheel assembly 118 areselected and controlled to have the desired background characteristics,which may be static or may vary in time. This background radiation is.of course, different and to be distinguished from the low backgroundradiation environment due to the low temperature produced by thecryoshroud 24 (FIGS. 1 and 2),

FIG. 6 is side elevational view, shown partially in section, of anotherversion 128 of the radiant energy source assembly 34 which can be usedwith the test apparatus of FIGS. 1 and 2. It can be readily seen thatthe source assembly version 128 is generally similar to the version 68(FIG. 3) except that a dual radiation guide 130 replaces the foldedreflector telescope source projector 96 in directing spectrallyundisturbed energy from an integrating sphere 132 to the focal plane ofcollimator mirror (FIG. 1). The guide 130 is joined at one end to theintegrating sphere 132 at which two adjacent output apertures or asuitably shaped sphere aperture similar to opening 92 (FIG. 4) may belocated. The guide 130 includes a cylindrical lower guide member 134 anda contiguous cylindrical upper guide member 136.

A dual variable aperture mask 138 is positioned just before the otherend of the guide 130 perpendicularly to the axes of the guide members134 and 136. The mask 138 is of the form of a thin disc sector havingits lower apex portion mounted to the end of the output shaft 140 of anelectric motor 142. The motor 142 is regularly reversed in direction byusing any suitable control means to oscillate the mask 138 in travelingbetween its angular width limits. Power to the reversible motor 142 can,for example, be periodically switched between forward and reverseterminals (windings) by an electrical, electronic or mechanicalswitching means.

FIG. 7 is a front elevational view of the movable disc sector mask 138.Five pairs of apertures 144 are provided in the mask 138, for example.The pairs of apertures 144 are equiangularly spaced from each other, andare progressively spaced closer together as illustrated. The motor 142(FIG. 6) can be suitably controlled to rotate the mask 138 eithercontinuously or in discrete steps in a counterclockwise direction sothat the radiant energy from the dual radiation guide 130 produces apair of small (point) sources from the pairs of apertures 144, which areprogressively moved radially closer together. This, ofcourse, provides ameasure of the resolving ability of the sensor 60 (FIG. 3) under test.In this instance, only one of the scanning mirrors 52 and 54 is used toprovide a radial scan (vertical in FIG. 7) at a reciprocatory rate whichis sufficiently high relative to the rotation rate of mask 138 toproduce an adequate exposure of the sensor 60 from both apertures ofeach pair of apertures 144. The detector array of sensor 60 includes,for example, eight (or 16) detectors arranged in two (or four) rows offour detectors each in the detector plane 62. The detectors of each rowcan be staggered with respect to those of an adjacent row, and scanningis normally perpendicular to the rows.

FIG. 8 is a front elevational view of the end of a single radiationguide 146 which is cooperatively structured to operate with thetransmission pattern (transparent portions) of a movable disc sectormask 148 indicated in phantom lines before the end of the guide. Theguide 146 replaces the dual radiation guide (FIG. 6) but is otherwisesimilar thereto. The normally open end of the guide 146 is closed by twosemicircular cover discs 150 and 152, leaving a narrow and verticaldiametrical slit 154 between the two cover discs. Radiant energy will,therefore, be emitted from the stationary slit 154 to the corresponding,radially outer, portion 156 of the adjacent movable mask 148 which canbe suitably rotated or oscillated on motor drive shaft 158.

FIG. 9 is a front elevational view of the movable disc sector mask 48which has indicated in phantom lines in FIG. 8. This mask 148 includes,for example, three wedge sections 160, 162 and 164 having differenttransmission patterns (transparent portions) 166, 168 and 170 providedrespectively in the radially outer portions 172, 174 and 176 thereof.The patterns 166, 168 and 170 are such that they function cooperativelywith the shape and dimensions of the stationary slit 152 (FIG. 8)provided at the end of the single radiation guide 146. The mask 148 canbe rotatably oscillated in a continuous motion by motor drive shaft 158between extremes of the sector mask or between extremes of any selectedone of the wedge sections 160, 162 and 164. Of course, the mask 148 canalso be rotatably driven in discrete steps rather than in a continuousmotion if desired. This may be especially desirable, for example, withthe pattern 170. Of course, with the sensor 60, only one of the scanningmirrors 52 or 54 is driven to provide a radial scan (vertically alongthe stationary slit 152 in FIG. 8) at a reciprocatory rate which is highrelative to the rotation rate of mask 148.

In the pattern 166, a curved transparent strip 178 intersects withanother curved transparent strip 180. The strip 178 extends from theupper left corner of the radially outer portion 172 of mask section 160to the lower right corner of such portion and is of regularlyalternating, equal length, strip widths. The strip 178 is curved suchthat a linear radial (vertical) travel is obtained with uniform(constant) speed rotation of the maks 148 and a regularly pulsatingsquare wave (or sine wave with suitable variation of strip widths)source output is provided. The strip 180 extends from the lower leftcorner of portion 172 to the upper right corner thereof and decreasesprogressively in strip width. The strip 180 is also curved such that alinear radial (vertical) travel is obtained with uniform (constant)speed rotation of the mask 148 and a regularly decreasing (size) sourceoutput is provided. Thus, a variable pulsating size source and adecreasing size source which progressively approach each other and thendraw apart can be provided by the pattern 166.

In the pattern 168, two curved intersecting transparent strips 182 and184 are provided in the radially outer portion 174 of mask section 162.The strips 182 and 184 are of similar and constant widths, and are eachcurved such that a linear radial (vertical) travel is obtained withuniform (constant) speed rotation of the mask 148. Thus, two sources ofsimilar size and which progressively approach each other and then drawapart can be provided by the pattern 168. The pattern 170, however,includes three radial columns 186, 188 and 190 of similarly sizedapertures. The apertures in column 186 are more distantly separated thanthose in column 190. In this instance, the mask 148 is preferably drivenin discrete steps from one column of apertures to the next so that eachof the aperture columns 186, 188 and 190 will be scanned in a stationarycondition. Thus, resolution measurements can be made with pattern 168simulating two dynamically moving target sources, and with pattern 170simulating spatially static target sources.

FIG. is a top plan view, schematically shown, of a monochromator type ofsource assembly 192 which replaces the source assembly version 68 (FIG.3) entirely when used. The monochromator source assembly 192 is capableof projecting monochromatic radiant energy, variable over a widewavelength range, into the collimator 26 (FIG. 1) of the apparatus 20. Ablackbody radiation sourk 1e 194 emits radiation which can be chopped bychopper 196 and reflected by plano mirror 198 to condenser mirror 200that focuses the radiation through filter wheel 202 onto entranceaperture 204. The filter wheel 202 includes different optical filtersfor blocking certain orders of radiation and can be adjusted by motor206 to position a selected filter before the entrance aperture 204.

The radiant energy passing through the entrance aperture 204 iscollimated and reflected by a spherical mirror 206 to diffractiongrating 208 which, in turn, diffracts and reflects the radiation toplano mirror 210. The plano mirror 210 directs the diffracted radiationto spherical mirror 212 which focuses it through central opening 213 ofmirror 210 onto exit aperture 214 located at the prime focus of theparabolic mirror 30 (FIGS. 1 and 2) of collimator 26. A plano mirror 216is mounted to the backing of the grating 208. By rotating the grating208 on its axis 218 over 180 degrees, the radiant energy from the source194 can be transmitted through the source assembly 192 withoutdiffraction by the grating 208. This provides a measure of the totalradiant energy involved.

FIG. 11 is a diagrammatic elevational view, shown largely in section, ofan all-reflective optical system for making spectral measurements ofsources and materi als with the use of a grating spectrometer 220located in a suitable portion of the collimated beam 48 (FIG. 2),utilizing the Cassegrainian type radiometer telescope 50 as the focusingdevice (collector) and the bolometer 56 of the calibration monitor asthe detector. The source assembly version 68 (FIG. 3) is illustrativelyused with the collimator 26. A scanning mirror 222 is interposed betweenthe collimator 26 output and the telescope 50 which has been mounted ina position to collect the radiation reflected by the scanning mirror.Energy is coupled into the spectrometer 220 by the telescope 50 and theoutput of the spectrometer is directed to the bolometer 56.

The spectrometer 220 is characterized by an on-axis optical system thatis advantageous in assuring ease of alignment, reliability of operationand high image quality. Spectral resolution attainable with the systemis high. The entrance aperture 224 to the spectrometer 220 is located atthe focal point of the telescope 50. Mirror 226 collimates and reflectsthe energy collected by the telescope 50 to grating 228 which, in turn,reflects the diffracted energy to mirrors 230 and 232, the

latter focusing the energy on exit aperture 234 and bolometer 56. Aliquid helium cooled, gallium doped, germanium bolometer detectorproviding a spectrally flat, high sensitivity, response can be used, forexample.

FIG. 12 is a top plan view, schematically shown largely in section, of auniversal version of source assembly 236 which novelly combines themonochromator type of source assembly 192 (FIG. 10) integrally into orwith the source assembly version 68 (FIG. 3). It can be readily seenfrom a comparison of the versions 68 and 236 that essentially mirrors76, 80, 82 and 84 of FIG. 3 have been replaced by spherical mirror 238,reflector cube 240 and spherical mirror 242 of FIG. 12. The sphericalmirrors 238 and 242 are similar, and the metallic cube 240 includes aplano specularly reflecting mirror 244 and three different diffractiongratings 246, 248 and 250, for example. The gratings 246, 248 and 250are normally used with reflector element 252 in the integrating sphere254 oriented in the specularly reflecting mode.

The reflector cube 240 can be rotatably adjusted by any suitable meanssuch as a motor (not shown) coupled to the mounting shaft 256 of thecube to place a selected one of the mirror 244 or gratings 246, 248 and250 in the reflecting position shown for mirror 244 in FIG. 12. Apolyhedron of more than six faces can, of course, also be used. Themirror 238 collimates the radiant energy from blackbody source 258 tothe mirror or grating (of cube 240) placed in the reflecting position,and the mirror 242 focuses the radiant energy reflected therefrom afterfurther reflection by the reflector element 252 in integrating sphere254 onto its exit aperture 260 placed at the back-focus of sourceprojector 262. Disc 264 includes a number of different sized exitapertures 260 arcuately spaced near its periphery and can be adjusted bymotor 266 to position a selected size exit aperture at the back-focus ofprojector 262.

By using blackbody sources and detectors which are secondary standardswith respect to National Bureau of Standards calibrations, absolutespectral measurements can be made to their assigned degree of accuracy.Thus, determinations of spectral or total irradiance, emittance,responsivity, noise figure, transmittance, reflectance and emissivitycan be made respectively on unknown sources detectors, sensors, filtersand optical elements. Further, in addition to standard responsivity andnoise measurements of space optical systems, other specializedmeasurements can be made with the advanced sensor evaluation and testapparatus. These include the determination of baffle evaluation ofoptical surfaces by interferometric and/or holographic methods, thetransient response of detector-amplifier subsystems and cross-talkmeasurements with respect to detector arrays.

It is to be understood that the exemplary embodiments of this inventionas described above and shown in the accompanying drawings are merelyillustrative of, and not restrictive on, the broad invention and thatthe invention is not to be limited to the exact details of constructionshown and described, for obvious modifications may occur to personsskilled in the art.

What is claimed is:

1. For use in exoatmospheric environmental test apparatus including avacuum chamber for providing and maintaining a predetermined vacuumcondition therein, a cryoshroud within said vacuum chamber for providingand maintaining a predetermined temperature therein, an opticalcollimator contained in said cryoshroud, and a pair of scanning mirrors,a radiant energy source assembly comprising:

a source of radiant energy;

an integrating sphere including an entrance aperture and an exitaperture, and an adjustable reflecting element mounted therein, saidelement having a specularly reflecting surface and a diffuselyreflecting surface;

means for directing the radiant energy from said source into said spherethrough said sphere entrance aperture;

means for adjusting said element selectively to one of its orientationsfor specularly reflecting, diffusely reflecting, and integrating sphereoperations; and

a source projector including an entrance aperture and an exit aperture,said projector entrance aperture being coupled to said sphere exitaperture and said projector exit aperture being positioned at an inputopening of said collimator whereby radiant energy from said sphere isdirected by said projector into said collimator.

2. The invention as defined in claim 1 wherein said element includes atwo-faced plano mirror rotatably mounted in said sphere and having aspecularly reflecting surface on one side and a diffusely reflectingsurface on an opposite side, said two-faced plano mirror beingselectively adjustable to one of its orientations for specularlyreflecting the radiant energy directed into said sphere onto its exitaperture, diffusely reflecting the radiant energy directed into saidsphere onto its exit aperture, and integrating sphere operation in whichthe radiant energy directed into said sphere is unobstructed by saidtwo-faced mirror in reaching an internal wall surface of said sphere andthe diffusely reflecting surface of said two-faced mirror generallyfaces said sphere exit aperture.

3. The invention as defined in claim 1 wherein said means for directingthe radiant energy from said source into said sphere includes opticalmeans for focusing the radiant energy from said source into said sphereand onto its exit aperture after reflection by said element adjusted toone of its orientations or specularly reflecting and diffuselyreflecting operations.

4. The invention as defined in claim 1 wherein said projector includes ahousing having said projector entrance aperture therein, a projectorconcave spherical mirror having a central aperture aligned with andpositioned a predetermined distance before said projector entranceaperture, and a folding plano mirror having a central aperture alignedwith and positioned a predetermined distance before said projectorconverging mirror central aperture, said folding plano mirror centralaperture being located at the focal plane of said collimator wherebyradiant energy from said sphere enters said projector entrance aperture,passes through the central aperture of said projector concave sphericalmirror, is reflected by said folding plano mirror to said projectorconcave spherical mirror which reflects the radiant energy back throughsaid folding plano mirror central aperture and into said collimator, areduced image of said sphere exit aperture which coincides with saidprojector input aperture being formed in the central aperture of saidfolding plano mirror.

5. The invention as defined in claim 1 further comprising means forvarying the amount of radiant energy directed into said sphere.

6. The invention as defined in claim 1 further comprising a choppermeans positioned before said source for modulating the radiant energyemitted therefrom at a predetermined frequency.

7. The invention as defined in claim 2 wherein said means for directingthe radiant energy from said source into said sphere includes aconverging mirror for focusing the radiant energy from said source intosaid sphere, said converging mirror having a focal plane placed at saidprojector input aperture after reflection by said adjusted elementadjusted to one of its orientations for specularly reflecting anddiffusely reflecting operations.

8. The invention as defined in claim 4 further comprising variableaperture means mounted in said housing for varying the size of saidprojector input aperture.

9. The invention as defined in claim 5 wherein said varying meansincludes an attenuator adjustable to attenuate a selected beam portionof the radiant energy from said source being directed into said sphere.

10. The invention as defined in claim 1 further comprising a sensorunder test in said apparatus, and a variable background radiationgenerator for providing background irradiance broadly superimposed inthe detection plane of said sensor under test.

11. The invention as defined in claim 10 wherein said sensor includes atelescope and a detector located at the focal plane of said telescope,and said background generator includes a radiation source of variabletemperature and predetermined size aperture, a filter wheel having aplurality of spectral and spatially struc tured filters which can beselectively positioned before said background source aperture, and aCassegrainian type collimator assembly of short focal length fordirecting the background radiant energy parallel to the optical axis ofsaid sensor telescope and into a peripheral portion of the entranceaperture thereof whereby an enlarged image of said background sourceaperture is broadly superimposed on said detector located at the focalplane of said telescope.

12. The invention as defined in claim 11 wherein said backgroundgenerator further includes means for rotating said filter wheelselectively either in steps or continuously whereby said backgroundradiant energy can be varied in a predetermined manner according to thetype and sequence of filters mounted in said filter wheel.

13. The invention as defined in claim 3 further comprising means forcollimating the radiant energy from said source, and an adjustablereflecting structure including at least a specularly reflecting surfaceand a diffracting reflection surface, said structure being selectivelyadjustable to one of its orientations for specularly reflecting anddiffracting reflection operations to reflect the radiant energy fromsaid source to said optical focusing means.

14. The invention as defined in claim 7 further comprising means forcollimating the radiant energy from said source, and an adjustablereflecting structure including at least a specularly reflecting surfaceand a diffracting reflection surface, said structure being selectivelyadjustable to one of its orientations for specularly reflecting anddiffracting reflection operations to reflect the radiant energy fromsaid source to said con verging mirror.

15. The invention as defined in claim 13 wherein said structure includesa polyhedron having a plurality of specularly reflecting and diffractingreflection surfaces, said structure being rotatably mounted andselectively adjustable to one of its orientations for specularlyreflecting and diffracting reflection operations.

16. In a radiant energy source assembly, an integrating sphere structurecomprising:

a hollow sphere including at least one entrance aperture and an exitaperture, said sphere having a diffusely reflecting internal wallsurface; and

an adjustable reflecting element mounted in said sphere, said elementbeing selectively adjustable to one of an obstructing position forreflecting radiant energy entering said entrance aperture out of saidexit aperture and an unobstructing position for allowing the enteringradiant energy to impinge upon said internal surface to provide diffusedradiant energy out of said exit aperture.

17. The invention as defined in claim 16 wherein said element includes atwo-faced plano mirror rotatably mounted in said sphere and having aspecularly reflecting surface on one face and a diffusely reflectingsurface on the opposite face.

18. The invention as defined in claim 16 wherein said sphere has acompound diffusely reflecting internal wall surface, said internal wallsurface including a convex diffused wall surface portion locatedapproximately opposite diametrically to said entrance aperture fordiffusely reflecting the incoming radiant energy generally towards saidexit aperture.

1. For use in exoatmospheric environmental test apparatus including avacuum chamber for providing and maintaining a predetermined vacuumcondition therein, a cryoshroud within said vacuum chamber for providingand maintaining a predetermined temperature therein, an opticalcollimator contained in said cryoshroud, and a pair of scanning mirrors,a radiant energy source assembly comprising: a source of radiant energy;an integrating sphere including an entrance aperture and an exitaperture, and an adjustable reflecting element mounted therein, saidelement having a specularly reflecting surface and a diffuselyreflecting surface; means for directing the radiant energy from saidsource into said sphere through said sphere entrance aperture; means foradjusting said element selectively to one of its orientations forspecularly reflecting, diffusely reflecting, and integrating sphereoperations; and a source projector including an entrance aperture and anexit aperture, said projector entrance aperture being coupled to saidsphere exit aperture and said projector exit aperture being positionedat an input opening of said collimator whereby radiant energy from saidsphere is directed by said projector into said collimator.
 2. Theinvention as defined in claim 1 wherein said element includes atwo-faced plano mirror rotatably mounted in said sphere and having aspecularly reflecting surface on one side and a diffusely reflectingsurface on an opposite side, said two-faced plano mirror beingselectively adjustable to one of its orientations for specularlyreflecting the radiant energy directed into said sphere onto its exitaperture, diffusely reflecting the radiant energy directed into saidsphere onto its exit aperture, and integrating sphere operation in whichthe radiant energy directed into said sphere is unobstructed by saidtwo-faced mirror in reaching an internal wall surface of said sphere andthe diffusely reflecting surface of said two-faced mirror generallyfaces said sphere exit aperture.
 3. The invention as defined in claim 1wherein said means for directing the radiant energy from said sourceinto said sphere includes optical means for focusing the radiant energyfrom said source into said sphere and onto its exit aperture afterreflection by said element adjusted to one of its orientations orspecularly reflecting and diffusely reflecting operations.
 4. Theinvention as defined in claim 1 wherein said projector includes ahousing having said projector entrance aperture therein, a projectorconcave spherical mirror having a central aperture aligned with andpositioned a predetermined distance before said projector entranceaperture, and a folding plano mirror having a central aperture alignedwith and positioned a predetermined distance before said projectorconverging mirror central aperture, said folding plano mirror centralaperture being located at the focal plane of said collimator wHerebyradiant energy from said sphere enters said projector entrance aperture,passes through the central aperture of said projector concave sphericalmirror, is reflected by said folding plano mirror to said projectorconcave spherical mirror which reflects the radiant energy back throughsaid folding plano mirror central aperture and into said collimator, areduced image of said sphere exit aperture which coincides with saidprojector input aperture being formed in the central aperture of saidfolding plano mirror.
 5. The invention as defined in claim 1 furthercomprising means for varying the amount of radiant energy directed intosaid sphere.
 6. The invention as defined in claim 1 further comprising achopper means positioned before said source for modulating the radiantenergy emitted therefrom at a predetermined frequency.
 7. The inventionas defined in claim 2 wherein said means for directing the radiantenergy from said source into said sphere includes a converging mirrorfor focusing the radiant energy from said source into said sphere, saidconverging mirror having a focal plane placed at said projector inputaperture after reflection by said adjusted element adjusted to one ofits orientations for specularly reflecting and diffusely reflectingoperations.
 8. The invention as defined in claim 4 further comprisingvariable aperture means mounted in said housing for varying the size ofsaid projector input aperture.
 9. The invention as defined in claim 5wherein said varying means includes an attenuator adjustable toattenuate a selected beam portion of the radiant energy from said sourcebeing directed into said sphere.
 10. The invention as defined in claim 1further comprising a sensor under test in said apparatus, and a variablebackground radiation generator for providing background irradiancebroadly superimposed in the detection plane of said sensor under test.11. The invention as defined in claim 10 wherein said sensor includes atelescope and a detector located at the focal plane of said telescope,and said background generator includes a radiation source of variabletemperature and predetermined size aperture, a filter wheel having aplurality of spectral and spatially structured filters which can beselectively positioned before said background source aperture, and aCassegrainian type collimator assembly of short focal length fordirecting the background radiant energy parallel to the optical axis ofsaid sensor telescope and into a peripheral portion of the entranceaperture thereof whereby an enlarged image of said background sourceaperture is broadly superimposed on said detector located at the focalplane of said telescope.
 12. The invention as defined in claim 11wherein said background generator further includes means for rotatingsaid filter wheel selectively either in steps or continuously wherebysaid background radiant energy can be varied in a predetermined manneraccording to the type and sequence of filters mounted in said filterwheel.
 13. The invention as defined in claim 3 further comprising meansfor collimating the radiant energy from said source, and an adjustablereflecting structure including at least a specularly reflecting surfaceand a diffracting reflection surface, said structure being selectivelyadjustable to one of its orientations for specularly reflecting anddiffracting reflection operations to reflect the radiant energy fromsaid source to said optical focusing means.
 14. The invention as definedin claim 7 further comprising means for collimating the radiant energyfrom said source, and an adjustable reflecting structure including atleast a specularly reflecting surface and a diffracting reflectionsurface, said structure being selectively adjustable to one of itsorientations for specularly reflecting and diffracting reflectionoperations to reflect the radiant energy from said source to saidconverging mirror.
 15. The invention as defined in claim 13 wherein saidstructure includes A polyhedron having a plurality of specularlyreflecting and diffracting reflection surfaces, said structure beingrotatably mounted and selectively adjustable to one of its orientationsfor specularly reflecting and diffracting reflection operations.
 16. Ina radiant energy source assembly, an integrating sphere structurecomprising: a hollow sphere including at least one entrance aperture andan exit aperture, said sphere having a diffusely reflecting internalwall surface; and an adjustable reflecting element mounted in saidsphere, said element being selectively adjustable to one of anobstructing position for reflecting radiant energy entering saidentrance aperture out of said exit aperture and an unobstructingposition for allowing the entering radiant energy to impinge upon saidinternal surface to provide diffused radiant energy out of said exitaperture.
 17. The invention as defined in claim 16 wherein said elementincludes a two-faced plano mirror rotatably mounted in said sphere andhaving a specularly reflecting surface on one face and a diffuselyreflecting surface on the opposite face.
 18. The invention as defined inclaim 16 wherein said sphere has a compound diffusely reflectinginternal wall surface, said internal wall surface including a convexdiffused wall surface portion located approximately oppositediametrically to said entrance aperture for diffusely reflecting theincoming radiant energy generally towards said exit aperture.